I recently performed the following mod to my Holden Monaro (Pontiac GTO), my particular vehicle has the LS1 5.7lt V8. I replaced the Valve springs with 918's and replaced the standard Roller Rockers with Yella Terra 1.8:1 Rockers. I hope this helps those DIY fans like myself.

Installing the Valve Springs

Step 1:
Remove the engine cover(s), if you have them, unplug the main harness to the coil pack. Remove the coil packs by undoing the 10mm nuts and bolts which secure the assembly.

http://img84.imageshack.us/img84/3158/picture063w.jpg

http://img180.imageshack.us/img180/9500/picture064h.jpg

Step 2:
Loosen the 8mm rocker cover bolts, at which point the bolts are loose but do not come out, then remove rocker covers.

http://img19.imageshack.us/img19/8308/picture065s.jpg

Step 3:
Remove the 8mm bolts securing the factory rockers to the head. Once all the rockers are removed, the rocker rail will come out freely.

http://img94.imageshack.us/img94/4775/picture067e.jpg

Step 4:
We will need to pressurise the piston chamber we are working on, this helps to stop valves from falling into the piston chamber when the valve springs are removed. Remove all the spark plugs. Screw in an air hold fitting into the first cylinder you are going to work on.(If you don't have an air fitting, you can always modify an old plug, get the ceramic out and weld on a male air fitting.) Hook up an air compressed line to the fitting installed in the head.

Step 5:
Once the piston chamber is pressurised you can begin removing the two springs for that cylinder. At this stage you will need to fit some style of valve spring compressor. The spring compressor I am using, uses the two rocker bolts and their original holes in the head to secure the spring compressor, then a separate larger thread torques down a plate with recesses cut out to allow the collet removal after spring compression.

http://img38.imageshack.us/img38/4782/picture069a.jpg

Step 6:
Once all four collets are removed, loosen off the plate, remove the old springs and replace them with your new ones.

Step 7:
Torque the plate back down ensuring you don't come down on a valve stem or it will release the air pressure in the chamber and fall in. Install the collets and remove the spring compressor.

Repeat steps 4 through to 7 for all 16 springs.

Installing the Yella Terra 1.8:1 Roller Rockers

I did this at the same time as the spring change so the old rockers and the rail assembly had already been removed. If you are starting from the beginning, then repeat steps 1 to 3 as above.

http://img33.imageshack.us/img33/3641/p1000488s.jpg

Step 1:
With an upside down pair of rockers, fit both pedestals to the recesses in the rocker shaft. Stick both original rocker bolts through from underneath so they go through the pedestals.

http://img180.imageshack.us/img180/9070/picture073o.jpg

http://img38.imageshack.us/img38/8910/picture074it.jpg

http://img94.imageshack.us/img94/4662/060ytprep.jpg

Step 2:
Using your index finger to keep the pedestal and shim on the bolts, turn the rocker assembly over and insert bolts into their appropriate holes. Ensure the rocker sits correctly on its corresponding pushrod.

http://img63.imageshack.us/img63/7930/070ytinstall.jpg

Step 3:
Screw the rocker bolts in finger tight using an 8mm socket and extension. Be sure to tighten evenly as most rockers will begin to compress their spring to some degree and the last thing you need it to be distributing load unevenly on the rocker bolts.

http://img84.imageshack.us/img84/1121/picture072o.jpg

Step 4:
Tighten the rocker bolts using a normal ratchet until about medium tightness, at which point you break out the torque wrench and nip each of these bolts up to 22lb/ft or 30Nm.

http://img180.imageshack.us/img180/7749/picture075k.jpg

http://img245.imageshack.us/img245/7631/picture076j.jpg

After each bank of rocker was complete, I kicked the engine over (no coils connected) for a few seconds to listen for any bad noises. I also did this once each rocker cover was installed.

Step 5:
Install rocker covers, spark plugs and coil packs.

Step 6:
Start the engine and give it a few minutes to let it to find it's new idle, once again listening for any mechanical noises which weren't there before. Mine almost stalled, then adopted a very lumpy cammed idle which smoothed itself out within minutes.

The valve train noise at idle had reduced dramatically, but once again lesser km engine may not see much diffenece.

Once the engine was warm I took it for a casual drive at first which then progessed into a bit of 'spirited driving'. I did notice it pulled harder from lower down which continued through the rev range.

And there you have it. Hope this helps anyone interested in doing the same.

You should post this on ls1gto.com This page of the site is DEAD.